1. Field
Embodiments described herein relate generally to a semiconductor memory device such as MRAM (Magnetic Random Access Memory).
2. Background Art
In recent years, as semiconductor integrated circuits have higher packing densities and lower power supply voltages, memory cells may have more operating margin faults in MRAM memory macros.
For example, an MRAM cell includes a storage element and a transistor. The MRAM cell is connected to a word line and a bit line.
A reading operation of data in such an MRAM cell requires a signal from a reference bit line for comparison with a signal from the bit line connected to the MRAM cell to be read.
In some methods, a signal from a reference bit line is the mean value of two different states held in at least two storage elements.
In other methods, multiple MRAM memory arrays are prepared for signal candidates of reference bit lines. One of the reference bit lines is selected so as to have a maximum reading margin and then the signal of the selected bit line is used.